I don't expect much from 3CA because Jazz have overloaded towers in several places (speedtests to their own local Jazz servers gives you the antenna-to-device throughput; speedtest to another server and you'll get the actual bandwidth available on their backhaul).
I won't call this throttling - but think of it as your wifi speed and network speed.
Where there's no congestion, they're plenty fast. But when congestion kicks in, speeds go down to 2Mbps at times in different places when throughput is around 15Mbps. Faizabad (Pindi/Islamabad) is one place where they need to bolster speeds.
And also, in PTA's reports for sometime now, they say the other operators are able to retain calls on 3G whilst Jazz still has a huge chunk of calls falling down to 2G despite the call being initiated on 3G (on roads and cities, if you want to exclude inside buildings).
All the more reason why VoLTE for Jazz should be expedited asap (since others won't have that much of a problem retaining a good quality call). They have good quality 4G signals in most of their coverage areas - even in shoddy places, you can get a good amount of speed (latencies vary depending on the signal strength and it's wireless so that's secondary anyway) but tower congestion on Jazz is a massive issue.
Long story short - backhaul bandwidth is congested in many places, assuming good signal conditions. All speedtest results on Jazz are on their local servers, not off-network (which is how it should be measured anyway). Getting 50Mbps transmission speeds mean absolutely nothing when your real throughput is around 2mbps (Faizabad, some parts of Bahria).